How do you group objects together without joining them?
there are many ways to do this, if you group objects together you can then add a group instance of that group, this is an empty that controls all the geometry in that group.

Alternatively you could use an empty, parent everything to it and then disable the ability to interact with the objects.

You can also just parent everything to an object of your choice, probably the biggest one of the group, and control everything that way.

It depends what your objective is by grouping.